Fix an obvious bug in getsourcefilter()'s use of struct __msfilterreq; the kernel will return in msfr_nsrcs the number of source filters in-mode for a given multicast group. However, the filters themselves were never copied out, as the libc function clobbers this field with zero, causing the kernel to assume the provided vector of struct sockaddr_storage has zero length. This bug would only affect users of SSM multicast, which is shimmed in 7.x. Picked up during mtest(8) refactoring.
Fix an obvious bug in getsourcefilter()'s use of struct __msfilterreq;
the kernel will return in msfr_nsrcs the number of source filters
in-mode for a given multicast group.
However, the filters themselves were never copied out, as the libc
function clobbers this field with zero, causing the kernel to assume
the provided vector of struct sockaddr_storage has zero length.
This bug would only affect users of SSM multicast, which is shimmed
in 7.x.
Picked up during mtest(8) refactoring.

MFC after:	1 day

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase